1. Field of the Invention
The present invention relates to an inductor structure. More particularly, the present invention relates to an inductor structure that can improve the value of Q.
2. Description of Related Art
Generally, as an inductor acquires energy storing and releasing functions through electromagnetic conversion, the inductor can be used as an element for stabilizing current. Further, the inductor can be widely utilized, for example, in a radio frequency (RF) circuit. In an integrated circuit (IC), the inductor is a very important but challenging element. For the performance of an inductor, the requirement on the quality of the inductor is high, i.e., the inductor must have a high quality factor, which is represented by a value of Q. The value of Q is defined as follows:Q=ω×L/R 
where ω is the angular frequency, L is the inductance of a coil, and R is the resistance at a specific frequency taking the inductance loss into consideration.
Currently, many methods and techniques are available to integrate inductors with IC processes. However, in an IC, the limitation on the thickness of the inductor conductor and the interference of the silicon substrate to the inductor will also lead to poor quality of the inductor. In the conventional art, a thick metal is disposed on the top of the inductor to reduce the conductor loss, so as to improve the value of Q of the inductor. However, when the thickness of the metal increases to certain extent, the improvement on the value of Q becomes unapparent. Further, as the inductor is often disposed near the silicon substrate, the parasitic capacitance generated between the silicon substrate and the inductor will increase, and the resistance of the inductor will increase accordingly. Thus, much energy must be consumed, and the quality of the inductor is degraded. As a result, it has become the key point of the vigorous development in the industry to solve the problems in the process to raise the value of Q of the inductor and reduce the conductor loss.